As the process for production of carbon fiber, there is a well-known process which comprises subjecting a raw material fiber [e.g. a polyacrylonitrile (PAN)] used as a precursor fiber, to an oxidation treatment and then to a carbonization treatment to obtain a carbon fiber (see, for example, Patent Literature 1). The carbon fiber obtained thus has good properties such as high tensile strength, high tensile modulus and the like.
In recent years, composite materials produced using a carbon fiber [e.g. a carbon fiber-reinforced plastic (CFRP)] are finding ever increasing applications in various industries. The following requirements are becoming stronger particularly in industries such as sport, leisure, aerospace, automobile and the like.                (1) Higher performance (high strength and high modulus)        (2) Lighter weight (light fiber weight and low fiber content)        (3) Exhibition of higher properties in compounding of composite material (improvement in carbon fiber surface property and interface property)        
In order to obtain a composite material of higher performance in compounding of a carbon fiber and a matrix material (e.g. a resin), it is important that the matrix material is improved in properties; further, it is essential that the carbon fiber per se is improved in surface property, strength and modulus. That is, a composite material of higher performance (high strength and high modulus) can be obtained by compounding a carbon fiber having a high adhesivity to matrix material, with a matrix material to uniformly disperse the carbon fiber in the matrix material.
Investigations have been made heretofore on the improvement of carbon fiber in surface property, strength and modulus (see, for example, Patent Literature 2).
However, conventional carbon fibers are insufficient in performance for use in production of a composite material satisfying the above-mentioned higher performance.
Patent Literature 1: JP-A-2001-131833 (Claims, page 5)
Patent Literature 2: JP-A-2003-73932 (Claims)